1. Field of the Invention
The present invention relates to a self-exciting and self-detecting probe suitable for use in a DFM mode in which a lever of the probe is vibrated for operation and a scanning probe apparatus utilizing the same.
2. Description of the Related Art
When a surface configuration of a sample is to be measured using a scanning probe microscope for example, a dynamic measurement mode has been widely used in which configuration data on the sample surface is obtained by causing resonance at a cantilever of the probe to tap the sample surface lightly, and controlling the position of the cantilever in a Z-direction by with servo system on a feedback basis to achieve uniform tapping.
Therefore, when a sample is measured in the dynamic measurement mode, configurations have been used in which a piezoelectric body, such as PZT, is coupled to a cantilever body through physical contact to excite the cantilever.
Measurement data has been then obtained by vibrating the cantilever with a voltage signal applied to the piezoelectric body, applying a DC bias to a resistive body mounted in the vicinity of a base portion of the cantilever to obtain a detection signal in accordance with deflection of the cantilever, and extracting the detecting signal through a differential amplifier.
Thus, in conventional configurations, a cantilever is externally excited using a piezoelectric body. This has resulted in a problem is that transmission of vibrations tends to become unstable depending on the state of mechanical coupling between a piezoelectric body and a cantilever and in that the provision of an additional piezoelectric body makes the configuration of an apparatus complicated.
Further, since deflection of a cantilever has been detected by applying a DC bias to a resistive body used as a distortion sensor and by detecting a resultant change in a voltage as the deflection of the cantilever, sensitivity has been poor, and accurate measurement has not been possible because of significant variations attributable to the mounting state.
An operating point is present in the vicinity of a resonance frequency of a cantilever, and it is therefore difficult to achieve reproducibility of the operating point because of variations of the characteristics of the cantilever, which has resulted in another problem in that a stable operation can not be expected.
It is an object of the invention to provide a self-exciting and self-detecting probe in which the above-described problems with the prior art can be solved and a scanning probe apparatus utilizing the same.
In order to solve the above-described problem, according to the invention, there is provided a scanning probe apparatus for measuring a sample by vibrating a lever of a probe, characterized in that a probe having a resistive body provided on the lever thereof is used and in that a periodic bias signal is applied to the resistive body to vibrate the lever.
The resistive body may be provided by doping the lever with an impurity by means of ion implantation. Variations in the transmission of vibrations can be eliminated to achieve more stable excitation compared to excitation using an externally attached piezoelectric body. The period of the bias signal can be arbitrarily chosen, which makes it easier to set an operating point different from the resonance point of the lever.
In the above-described configuration, the resistive body may be used as a detecting element for detecting distortion of the lever.
The above-described configuration may be modified by providing a separate detecting element for detecting distortion of the lever in addition to the resistive body.
In the above-described configuration, a reference resistive body having the same configuration as the resistive body may be provided in the vicinity of the lever, and the reference resistive body may be used for temperature compensation for detecting distortion of the lever.
When the reference resistive body is used for temperature compensation during the detection of distortion of the lever, a configuration may be employed in which the same AC bias is applied to both of the reference bodies.
If a bias signal having a periodically changing amplitude, such as an alternating current, is used to detect distortion of the lever, the detection can be carried out with a preferable signal-to-noise ratio, and highly accurate measurement can be performed according to various wave detecting methods using components such as amplitudes, phases, and frequencies. This makes it possible to detect signals at low levels and to provide a scanning probe apparatus capable of measurement with high resolution and accuracy.